Volume Controller using Knob (Potentiometer)

Building a Physical Volume Knob for AOSP on Raspberry Pi 5

In this talk, I'll show how I connected a rotary potentiometer to a Raspberry Pi 5 running AOSP Android 15 and made it control the media volume — using a 250-line C++ daemon in the vendor layer, with zero changes to the Android framework.

Along the way we hit real walls: a library blocked by VNDK, build and runtime errors, three SELinux types that don't exist in AOSP 15, and a hardware bus number that wasn't what we expected.

• How the AOSP vendor layer is structured and what belongs in it

• How to read hardware sensors from a native C++ daemon using standard Linux kernel ABIs

• How uinput works and why it is sometimes the right way to talk to Android audio from vendor code

• How to write and debug SELinux policy for a vendor service from scratch

• The difference between BOARD_VENDOR_SEPOLICY_DIRS and PRODUCT_PRIVATE_SEPOLICY_DIRS and why it matters

• How to iterate on a vendor service without reflashing the entire image